Function connectMongoDB

If the host/port form is used, default settings will be used, which enable
safe updates, but no fsync. By specifying a URL instead, it is possible to
fully customize the settings. See
http://www.mongodb.org/display/DOCS/Connections for the complete set
of options. Note that 'sslverifycertificate' is only present in some client
bindings, including here.

Note that the returned MongoClient uses a vibe.core.connectionpool.ConnectionPool
internally to create and reuse connections as necessary. Thus, the
MongoClient instance can - and should - be shared among all fibers in a
thread by storing in in a thread local variable.

Authentication

Authenticated connections are supported by using a URL connection string
such as "mongodb://user:password@host". Note that the driver currently
only supports the "MongoDB-CR" authentication mechanism. Since new
MongoDB versions, starting with 3.0, default to the new "SCRAM-SHA-1"
method, it is necessary to manually switch to the old method. See
http://stackoverflow.com/questions/29006887/mongodb-cr-authentication-failed
for more information.